1. Field of the Invention
The invention relates to a capacitor structure, and more particularly to a metal-oxide-metal (MOM) capacitor structure.
2. Description of Related Art
Capacitors are essential and fundamental devices in the current semiconductor industry. The metal-oxide-metal (MOM) capacitor is a common capacitor structure and has a basic design of filling an insulating medium between the metal plates adopted as electrodes, such that a capacitor unit is formed between every two adjacent metal plates and the insulating medium therebetween.
Since the capacitance of the MOM capacitor is positively proportional to the area of the electrode and inversely proportional to the distance between two electrodes, the capacitance can be increased by reducing the thickness of the insulating medium between the electrodes, or increasing the surface area of the electrodes, and so on in the design of the capacitor structure.
The methods of increasing the surface area of the electrodes include a multi-layer capacitor structure which adopts multiple layers of metal electrodes to increase the surface area of the electrodes. However, the uniformity of the medium layer, complicated fabrication steps, and the stability of the fabrication are difficult to control.
With the demands for miniaturizing semiconductors, the integration of the integrated circuits is becoming higher. Therefore, researches have been conducted to improve the capacitor structure for increasing the capacitance in a unit area of the capacitor structure under the current fabrication specification. In order to increase the capacitance in the unit area of the capacitor structure effectively, an optimal capacitor structure design has to be introduced.